This specification relates to three-dimensional (3D) printing.
Photopolymer-based 3D printers that use bottom-up illumination can project light upwards through an optically transparent window into a vat of photo-reactive resin to cure at least a portion of the resin. Such printers can build a 3D structure by forming one layer at a time, where a subsequent layer adheres to the previous layer. The light can be patterned to cause some portions of the resin to cure and other portions not to cure, thereby creating substructures of the 3D structure.